The present invention relates to water pumps and more particularly, to a combination pressure tank, sealed-in envelope, and pump.
The purpose of a water pumping system is to provide water under pressure by employment of a power operated pump, together with devices to control the pump and store the water. Most commonly, the system is powered by an electric motor and incorporates a closed pressure tank. The four essential elements of such a system are: (1) pump; (2) tank; (3) pressure control; and (4) air control.
In the past, problems have existed in providing satisfactory and efficient water pumping systems, for example, for use in pumping water from water wells. The present invention is directed to improving such pumping systems by modifying the pump and tank design to incorporate an additional element of equipment.
The function of the tank in an automatic water system is to store water under pressure and make it available upon demand. Essentially, the water pressure is provided by a form of storable energy contained within the tank, air under pressure, which acts upon the water so as to force it from the tank to the point of use. When water is drawn from the tank, the air within the tank expands. When water is brought into the tank by a pump, the air is compressed. In this manner, water under pressure can be provided from the tank independent of whether the pump is running at that moment.
The water tank, therefore, not only prevents rapid cycling of the pump and pump motor which would otherwise occur instantaneously with water being drawn out, but it also provides water under pressure for delivery between pump cycles. However, the use of air under pressure to create water pressure carries with it a problem. Specifically, the difficulty is that of the mixing of air and water in the tank. This results from a basic characteristic of water which is its ability to absorb air. Thus, to insure a continuing pumping operation, it is necessary either to replenish the absorbed air, or in the alternative, to reduce or prevent air absorption.
The conventional pressure storage tank is a hydropneumatic tank in which both water and air are stored within the tank with no barrier separating the water from the air. This requires the use of an air volume control in order to maintain a predetermined amount of air within the tank. Periodic changes in air volume are the result of both the air being absorbed by the water and excess air within the pumped water being introduced into the tank. Moderate air volume changes can be regulated but excess air can cause the system to become air-bound or waterlogged in which case water pressure is lost. Recognition of the problem of waterlogging has led to alternative approaches in the design of hydropneumatic storage tanks. These alternatives include the floating wafer type of storage tank, the diaphragm type tank and the bag or envelope type tank.
The floating wafer tank uses a wafer or disc which rides on the surface of the water so as to reduce the air and water contact area. The tank still requires an air replenishment system, however, since the wafer does not completely separate the air from the water.
The diaphragm type pressure storage tank uses a sealed-in flexible separator which completely isolates the pressurized air from the water. Water pressure is maintained by the pressure of the air against the diaphragm. Typically, the tank is pre-charged at the factory to approximately the pump start pressure-a predetermined low pressure in the water system which activates the pressure switch to energize the motor and start the pump. An air volume control or air charging system is not required on this type of tank because of the air and water separation.
The bag or envelope type of pressure storage tank is similar to the diaphragm type tank with the exception that either the air or the water, depending on the configuration, is contained wholly within the envelope. This design is well known in the art and is recognized as a highly efficient means of both pressurizing the water system and eliminating waterlogging.
Although the bag or envelope can be used as the storage vessel for either the air or the water, the advantage of using the envelope as the water container is that the envelope will impart neither odor nor taste to the water as would be likely with the tank. Furthermore, the bag forms a completely corrosion-proof reservoir.
The significance of the envelope concept, however, is in its elimination of the air absorption problem. This results in the cycling frequency of the pump being greatly reduced, thereby increasing pump and motor life. In addition, there is no need for the complexity of air controls and air replenishment systems which characterize the conventional hydropneumatic storage tank.
Distinct from the incorporation of the envelop in the tank, the prior art also reflects important modifications relating to the physical placement of the pump. Prior systems, for example described in U.S. Pat. No. 2,403,555, have adapted the pump to fit within the tank to provide more satisfactory operation. In particular, the placement of the pump can be such as to insure that the pump will be submerged in water at all times with the result that the pump will be self-priming. A further advantage of the pump being internal to the tank is that the physical character of the pump and tank system will be that of a single unit very compact in configuration.
It is evident, therefore, that distinct advantages accrue from the use of the water envelope pressure tank and the internal pump system. Currently, there is no known system which incorporates both features. Thus, the present invention relates to a combination pressure tank envelope and internal pump system which carries with it the significant benefits of these two concepts.